Return Anonymous Type from a function

Question

Can I use an anonymous type as a return type in a Function, and then stuff that returned value into an array or collection of some sort whilst also adding an additional fiel

Answer 1

From C#7 you can return a list of tuples:

private IEnumerable<(string, string)> GetRowGroups(string columnName)
{
    return from table in _dataSetDataTable.AsEnumerable()
           group table by new { column1 = table[columnName] }
           into groupedTable
           select (groupedTable.Key.column1, groupedTable.Count());
}

You can even give the members of the tuple names:

private IEnumerable<(string groupName, string rowSpan)> GetRowGroups(string columnName)
{
    return from table in _dataSetDataTable.AsEnumerable()
           group table by new { column1 = table[columnName] }
           into groupedTable
           select (groupedTable.Key.column1, groupedTable.Count());
}

However you need System.ValueTuple from the Nuget Package Manager.

Anyway I suggest to give things a clear name that includes what their purpose is, in particular when this is part of a public API. Having said this you should consider to create a class that holds those properties and return a list of that type.